3-18 Turn off the power before connecting alligator clips to any circuit. Never use your finger to test a "hot" line. Use approved voltmeters or other voltage-indicating devices. High Voltage Precautions In addition to observing the general precautions just discussed, you must observe the following additional precautions when working with high voltages: Do NOT work with high voltage by yourself; have another person (safety observer), qualified in first aid for electrical shock, present at all times. This individual, stationed nearby, should also know the circuits and location of the switches controlling the equipment, and should be given instructions to pull the switch immediately if anything unforeseen happens. Always be aware of the nearness of high-voltage lines or circuits. Use rubber gloves where applicable and stand on approved rubber matting. Not all so-called rubber mats are good insulators. Always discharge the high voltage from components or terminals by using a safety probe. Do NOT hold the test probe when circuits over 300 volts are tested. Soldering Irons When using a soldering iron, always keep in mind the following precautions and procedures: To avoid burns, ALWAYS ASSUME that a soldering iron is hot. Never rest a heated iron anywhere but on a metal surface or rack provided for this purpose. Faulty action on your part could result in fire, extensive equipment damage, and serious injuries. Never use an excessive amount of solder, since drippings may cause serious skin or eye burns. Do not swing an iron to remove excess solder. Bits of hot solder that are removed in this manner can cause serious skin or eye burns. Hot solder may also ignite combustible materials in the work area. When cleaning an iron, use a cleaning cloth, but DO NOT hold the cleaning cloth in your hand. Always place the cloth on a suitable surface and wipe the iron across it to prevent burning your hand. Hold small soldering jobs with pliers or a suitable clamping device to avoid burns. Never hold the work in your hand. Do not use an iron that has a frayed cord or damaged plug. Do not solder components unless the equipment is disconnected from the power supply circuit. Serious burns or death can result from contact with a high voltage.